1. Field of the Invention
The present invention relates to a manufacturing method of a mask for an exposure apparatus used to expose fine patterns in a manufacturing process of semiconductor integrated circuits, etc., and more particularly to a manufacturing method of a mask used in an electron beam proximity exposure apparatus in which the mask having apertures corresponding to a pattern to be exposed is disposed in proximity to a surface of an object such as a semiconductor wafer, the mask is irradiated with an electron beam, and exposure of the pattern with the electron beam having passed through the apertures is thereby performed.
2. Description of the Related Art
Attempts are being made to enhance integration degrees of semiconductor integrated circuits and finer circuit patterns are desired. Presently, a limit of the finer circuit patterns is defined mainly by exposure apparatuses, and a stepper, which is an optical exposure apparatus, takes various measures such as a light source that emits rays having shorter wavelengths, a larger NA (numerical aperture) and a phase shift method. However, much finer circuit patterns involve various kinds of problems such as a rapid increase of production costs. New types of exposure apparatus such as an electron beam direct lithography apparatus and an X-ray exposure apparatus have been therefore developed, but there still remain many problems in terms of stability, productivity, cost, etc.
An electron beam proximity exposure system is conventionally under research and development, since the exposure principle thereof is simple, as xe2x80x9cHigh Throughput Submicron Lithography with Electron Beam Proximity Printingxe2x80x9d (H. Bohlen et al., Solid State Technology, September 1984, pp. 210-217) (hereinafter referred to as literature 1) exemplifies. However, it was thought that it was of no practical use since it was difficult to eliminate the proximity effect peculiar to the electron beam.
U.S. Pat. No. 5,831,272 (corresponding to Japanese Patent No. 2951947) and xe2x80x9cLow energy electron-beam proximity projection lithography: Discovery of missing linkxe2x80x9d (Takao Utsumi, J. Vac. Sci. Technol. B 17(6), November/December 1999, pp. 2897-2902) disclose an electron beam proximity exposure apparatus that overcomes the above-mentioned problems and is usable for processing with very fine resolution at a mass production level.
FIG. 1 is a view showing a fundamental configuration to realize the electron beam proximity exposure apparatus disclosed in U.S. Pat. No. 5,831,272. Referring to this drawing, the electron beam proximity exposure apparatus disclosed in U.S. Pat. No. 5,831,272 will be briefly described. As shown in FIG. 1, in a column 10 are disposed an electron gun 12, which includes an electron beam source 14 emitting an electron beam 15, a shaping aperture 16, and a condenser lens 18 collimating the electron beam 15; scanning means 20, which includes a pair of main deflecting devices 22 and 24 and scans with the electron beam parallel to the optical axis; an object mask (hereinafter simply referred to as a mask) 30, which has apertures corresponding to an exposed pattern; and an object (a semiconductor wafer) 40, of which surface is coated with a resist layer. The mask 30 has a film 32 with the apertures formed at the center within a thick rim 34, and the object 40 is disposed so that the surface thereof is in proximity to the mask 30. In this state, when the electron beam is vertically applied to the mask, the electron beam passing through the mask""s apertures is applied to the resist layer 42 on the surface of the object 40. The entire surface of the film 32 on the mask 30 is scanned by deflecting the electron beam 15 (A, B, and C in FIG. 1 denote the deflected beam toward three points) with the scanning means 20, so that all aperture patterns of the mask 30 are exposed. The scanning means 20 has subsidiary deflecting devices 51 and 52, which slightly lean the electron beam, and is used to position the mask 30 and the object 40 and to correct a difference between the exposure positions due to distortion of the mask and distortion of the object.
The mask for an electron beam proximity exposure apparatus must not have any defect. Accordingly, prior to be used, a manufactured mask is inspected whether it has no defect. Although a correction device corrects defects if any, some of the defects are uncorrectable. If the mask has the uncorrectable defects, it is required to dispose of the mask and to form a new mask without defect.
Variety kinds of factors cause defects of the mask, and the major one of the factors is contamination with dust (particles). On the same manufacturing conditions, an incidence of the defect caused by dust is in proportion to the area of the mask. Therefore, manufacture of bigger masks involves a higher incidence of the defect.
The mask for the electron beam proximity exposure is manufactured by exposing the pattern by a conventional electron beam exposure apparatus that can expose desired patterns. Such an apparatus takes an extremely long time for exposing patterns with high quality, and the costs of the masks are thereby increased. As described above, if the mask has the uncorrectable defects, it is required to dispose of the mask and to expose a new mask for a long time until a defectless mask is obtained. It produces a problem in that the production costs of masks are even increased.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of a method for manufacturing masks for the electron beam proximity exposure at reduced costs.
The inventors of the present invention have directed their attention to the features that the electron beam proximity exposure apparatus is an actual-size exposure apparatus, an exposed pattern is identical with a pattern of the mask, and the electron beam proximity exposure apparatus can be used to copy the masks.
The method for manufacturing a mask for the electron beam proximity exposure according to the present invention is characterized in method for manufacturing a mask which is used in an electron beam proximity exposure apparatus comprising an electron beam source which emits a collimated electron beam, the mask having an aperture which is arranged on a path of the electron beam, and a stage which holds and moves an object, wherein the mask is arranged in proximity to a surface of the object and a pattern corresponding to the aperture of the mask is exposed on the surface of the object with the electron beam having passed through the aperture, the method comprising the steps of: dividing the mask into a plurality of partial areas, and forming a plurality of partial masks which have apertures with patterns identical with the plurality of partial areas, respectively; and manufacturing the mask by exposing the patterns of the plurality of partial masks on corresponding positions of a mask substrate in an electron beam proximity exposure method.
The patterns of the partial masks should be exposed at predetermined positions with respect to each other, and it is preferable that each of the plurality of partial masks has a positioning mark.
As described in the above, the mask for the electron beam proximity exposure is a very thin film, which is required to have an excellent flatness. Then, it is necessary to form a thin film on the surface of the film to apply a force in the direction of it shrinking so that a stress to tense the thin film portion is applied from the thick portion around the mask. However, the film for stressing causes a very small distortion on the aperture pattern, which results in a difference between the actual aperture pattern and a desired pattern.
As disclosed in U.S. Pat. No. 5,831,272, etc., the electron beam proximity exposure apparatus can correct a small distortion of the mask by adjusting a direction of the electron beam applied to the mask. Then, after the manufacturing of the partial mask, it is preferable to measure an amount of distortion of the pattern thereof, and to perform the exposure of the mask while correcting the amount of the distortion.
Since the partial masks are masks of areas into which a mask of size of one chip is divided, they are smaller than the mask of size of one chip. Accordingly, if a substrate on which the mask of size of one chip can be formed or a bigger substrate is used as a partial mask substrate, a plurality of partial masks can be formed separately from each other. For example, the partial mask substrate big enough to arrange all partial masks separately from each other is used, so that all partial masks are separately formed on a single partial mask substrate. If no uncorrectable defect is detected in all partial masks on inspection, a pattern of one mask is exposed by using only the partial mask substrate when a moving mechanism for the partial mask substrate is provided on the electron beam proximity exposure apparatus. In this case, it is unnecessary to take the partial mask substrate out the apparatus to replace it while exposing the pattern of one mask, so that it can reduce a time for performing the exposure.
If one or more of the partial masks has an uncorrectable defect, partial masks concerning the uncorrectable defect are formed as many as possible on the second partial mask substrate. For example, when the partial mask substrates on each of which sixteen partial masks can be formed are used, and if there are four pieces of the partial mask with uncorrectable detects on the first partial mask substrate, four pieces of the partial mask each corresponding to each of the partial masks with the uncorrectable defects can be formed on the second partial mask substrate. On account of a low incidence of uncorrectable defects on all the four partial masks, all patterns of the mask are generally exposed by using the two pieces of the partial mask substrates.
The use of the partial mask substrate that can have more partial masks so as to form a plurality of pieces of each the partial mask on a single partial mask substrate improves a chance of providing a complete set of defectless partial masks on the single partial mask substrate.